Height-Tailored Projections for Composite Joint Load Transfer
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Solution Overview
Problem
Current methods for joining metallic or thermoplastic components with composite materials, such as fasteners and adhesive bonds, are weak in pull-off direction and prone to de-lamination, limiting their suitability for aerospace applications, and existing surface feature generation techniques can compromise fatigue life and are difficult to optimize.
Innovation Solution
A method of forming an array of projections with varying profiles on the bond surface of one component, which are embedded into a laminate composite, allowing for progressive load transfer into multiple plies, reducing stress concentrations and enhancing tensile strength.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If fasteners are used to join metallic or thermoplastic components to composite laminates, then the joint can be easily assembled, but the joint becomes weak in pull-off direction and causes de-lamination around fastener holes
Solution Approach 1:
The patent replaces the mechanical fastening system (screws, bolts, rivets) with an additive manufacturing system that directly fabricates three-dimensional projections on the bond surface. These projections mechanically interlock with the composite laminate during co-curing, eliminating the need for separate fasteners while achieving superior pull-off strength through progressive load transfer into multiple laminate plies.
2Strength
If adhesive bonds are used to join metallic components to composite laminates, then the joint can be formed without holes, but the bond performs poorly in peel and tension and fails with little warning
Solution Approach 1:
The patent creates a hybrid joint structure combining metallic or thermoplastic base material with additive-manufactured projections that extend into the composite laminate. This composite approach integrates two different joining mechanisms: the projections provide mechanical interlocking with progressive load transfer, while the surrounding adhesive material provides stress distribution and failure warning through gradual degradation before catastrophic failure.
3Strength
If surface features are generated by power-beam to increase bond surface area, then the bond strength is improved, but crack initiators are generated that adversely affect fatigue life
Solution Approach 1:
The patent replaces the power-beam surface modification process with additive manufacturing of three-dimensional projections. The additive process builds material layer-by-layer to create controlled geometric features with smooth surfaces and optimized profiles, eliminating the crack-initiating surface defects that result from power-beam material displacement and flick-up operations.
4Strength
If identical projections are closely packed to increase bond surface area, then the bond strength is improved, but stress concentrations occur around the projections leading to net section failure
Solution Approach 1:
The patent applies local quality by varying the projection profiles across different locations in the array. Projections closer to the bond surface have smaller heights, while those deeper in the laminate have larger heights. This gradient distribution optimizes load transfer at each depth level, distributing stress more evenly throughout the laminate thickness and preventing concentration at any single location.
Solution Approach 2:
The patent changes the geometric parameters of the projections, specifically the height dimension, as a function of position in the array. This parameter variation creates a progressive load transfer mechanism where each projection engages with laminate plies at different depths, distributing the axial load across multiple plies and reducing stress concentrations that would occur with uniform projection heights.
Data Source
AI summary
A method of joining a first component to a second component, the method comprising forming an array of projections extending from a bond surface of the first component, the projections having a plurality of different profiles; and embedding the array of projections in the second component formed of a plurality of laminate plies, wherein each projection profile is adapted to best transfer load into a respective one of the laminate plies. The resultant joint is able to transfer load more progressively between the two components leading to improved tensile strength.